The National Weather Service has issued a flash flood watch for all of southeastern Louisiana, including New Orleans and Baton Rouge, beginning Friday night, with forecasters predicting widespread rainfall totals of 3 to 5 inches, with locally higher amounts of greater than 8 inches through Sunday night.

View full sizeForecast information for the New Orleans area through Sunday.National Weather Service

A slow moving cold front will approach the region Friday night and move into southeastern Louisiana on Saturday, where it will stall along the coast on Saturday night.

"Scattered to numerous thunderstorms are expected to develop this afternoon and linger into the overnight hours as a cold front approaches the area," said a hazardous weather outlook message issued this afternoon by the Slidell office of the National Weather Service. "Severe weather is not expected (Friday afternoon and evening), but a few stronger storms will be possible.

"The main impact from these thunderstorms will be frequent lighting strikes and locally heavy downpours," the forecast said.

With abundant moisture already in place, the result of wet air streaming north from the Gulf of Mexico, combined with additional moisture moving east from the remains of Pacific Hurricane Manuel.

That will allow the trough of low pressure accompanying the front to trigger showers and thunderstorms that will efficiently produce rainfall. Areas along and northwest of a line from Houma to Franklinton appear to have the greatest risk of heavy rainfall overnight Friday and Saturday, with locations to the southeast of that line seeing the highest risk beginning Saturday night and lasting through Sunday.

The rainfall accompanying frontal system is likely to cause flooding of streets, bayous, canals and poorly drained areas in locations where individual showers and thunderstorms stall or repeated storms pass over.

Forecasters warn the rainfall could extend through Thursday, when an upper level ridge of high pressure is expected to build over the south.